The proposal is designed to study mechanisms of intestinal transport with special emphasis on calcium. We will attempt to delineate mechanisms by stimulation of transport in contrast to the more usual studies with metabolic inhibitors. Adaptive changes in transport occuring in remaining gut following extensive intestinal resection will be studied. Use of these models has been limited. In vivo studies will employ in situ perfusions of segments of small and large intestine using radionuclide tracer initially present in either the intestinal lumen or in the preloaded animal. In vitro studies will utilize gut sacs and the short circuit current technique of Ussing and Zerahn modified for intestinal tissues: planar tissue sheets will be clamped between half cells and incubated with identical media on each side. Radionuclide tracer will be added to one side and electrical gradients neutralized by an external current source. These methods will allow quantitation of transport and unidirectional mucosal cell fluxes under in vivo and in vitro conditions, the ready separation of active from non-active transport and studies of effects of electrical as well as chemical gradients across intestinal mucosa. As well as the studies of calcium, transport of other luminal substrates will be investigated by these methods.